1. Technical Field
This invention relates to railway vehicles and steering trucks therefor. More particularly, this invention relates to railway locomotives and motorized self-steering radial trucks for locomotive use.
2. Background
Conventional railway truck designs comprising a pair of laterally spaced side frames and a transom extending transversely there between have become the standard in many railway industry applications. These trucks include axle and wheel assemblies which rotatably support the frame by means of bearing housings at the ends of the axles. Problems encountered with these conventional trucks include the tendency for the wheel sets to traverse curves in a non-radial orientation and with much wheel flange to rail rubbing contact. Furthermore, the wheel sets may tend to slide during negotiation of track curves. Such rubbing contact and wheel sliding result in undesirably high wheel and rail wear, and the flange rubbing in particular may produce a tendency for the wheel to climb the rail. In addition, improper wheel set tracking in curves may result in track misalignment.
Other related problems occur when conventional trucks traverse straight or tangent runs of track. For example, a rigid wheel axle set, having conventional tapered conical wheels, when displaced laterally from the center line of a run of straight track, executes two simultaneous motions; first, the wheel set moves toward its equilibrium (center) position under the influence of gravity, and secondly, the high side wheel, rolling on a larger diameter than the low side wheel, moves along the rail faster than its partner, causing the wheel set to yaw. Given the proper set of circumstances, this motion may become a sustained harmonic oscillation known as hunting. The hunting tendency is transmitted to the truck and causes an oscillatory yawing motion of the truck about its center of rotation, resulting in additionally high wheel and rail forces and wear.
These problems have been recognized in the prior art and a variety of self steering railway truck designs which purport to allow the wheel sets to track without sliding and without undue flange rubbing during negotiation of curves, and with minimal adverse consequences resulting from hunting. These designs typically mechanically couple the two end axles of the truck through traction rods pivotally connected to the axle bearing housings so that when curved track operation induces a rotation, or yaw, of one axle, a mechanical linkage including the traction rods induces an opposite yawing of the trailing truck axle. In this way, the wheel sets more closely track the curvature of the track and wheel and track wear is minimized.
One example is Goding, U.S. Pat. No. 4,765,250, which teaches a method for inducing an "equal and opposite" rotation, or yaw, of one truck axle in response to the yawing of another truck axle when the truck is encountering a curve. Four traction rods, pivotally connected to the bearing housings of the two axles, connected at their other ends to two transversely mounted steering beams, and aligned generally parallel to the truck longitudinal axis, transmit the tractive force to a lower end of respective vertical shafts. Attached to the top of each of the vertical shafts are opposing crank arms which themselves are interconnected by a diagonal link. As one axle yaws, that yawing motion is transmitted via the traction rods, steering arms, vertical shafts, crank arms and diagonal link to induce an opposite yawing motion in the other axle.
A major problem with self-steering railway truck designs is that freeing the axles so that they may yaw and allow the wheel sets to more closely follow the track curvature, and thereby minimize wheel flange and track wear, at the same time permits the axle and wheel sets additional lateral displacement freedom, thereby increasing the potential for truck hunting. In other words, the objectives of wheel set self-steering and truck hunting minimization work are conflicting. One approach to this problem has involved rigidizing the truck frame, in addition to using resilient pads between the truck framing and the axle and wheel sets, thereby inhibiting lateral displacement of the axle and wheel sets. This arrangement still allows a limited measure of self steering of the axle and wheel sets. However, often there is only limited suppression of truck hunting while self steering is compromised.
Accordingly, the object of this invention is to provide a self-steering railway truck in which hunting, with its concomitant adverse affects, is minimized, by inhibiting wheel set lateral displacement.
Another object of this invention is to provide a self-steering railway truck in which hunting is minimized while permitting self-steering axle yaw action.